Storing signature time in the contract

[biern]

From our recent discussions it turned out that signature time might be crucial for some use cases.
(eg. proving that one have created a file / photo / results before a given time)
What's your opinion on storing this value in the contract?
I know that it's possible to read the signature time now by fetching the events, but having this stored in the contract will make the information available instantaneously for the users, without involving any extraneous, possibly long-lasting requests.